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Spin valves based on materials in which the spin-flip is suppressed by the spatial separation of charge carriers, while maintaining electric neutrality in the valve volume, are considered. The possibility of using these valves as electric batteries is discussed. It is shown that if the potential difference across the valve is controlled, incommensurability effects such as the "devil's staircase" may be expected, which are associated with the Coulomb interaction and redistribution of electrons occurring while the battery is charged and discharged. The effects of the emergence and vanishing of spontaneous spin polarization of conduction electrons with a change in the Fermi level in the valve are predicted. Such spin valves can also be used in implementing spintronic memory cells, supercapacitors, and similar devices.

The review is focused on our recent predictions of nontrivial physical phenomena taking place in the nanostructure single-layer grapheme on ferroelectric substrate, which are related with magnetic field. In particular we predicted that 180-degree domain walls in a strained ferroelectric film can induce p-n junctions in a graphene channel and lead to the unusual temperature and gate voltage dependences of the perpendicular modes {\nu} of the integer quantum Hall effect. The non-integer numbers and their irregular sequence principally differ from the conventional sequence {\nu}= 3/2, 5/3. The unusual v-numbers originate from significantly different numbers of the edge modes, {\nu}1 and {\nu}2, corresponding to different concentration of carriers in the left (n1) and right (n2) ferroelectric domains of p-n junction boundary. The difference between n1 and n2 disappears with the vanishing of the film spontaneous polarization in a paraelectric phase, which can be varied in a wide temperature range by an appropriate choice of misfit strain originated from the film-substrate lattice mismatch. Next we studied the electric conductivity of the system ferromagnetic dielectric - graphene channel - ferroelectric substrate. The magnetic dielectric locally transforms the band spectrum of graphene by inducing an energy gap in it and making it spin-asymmetric with respect to the free electrons. It was demonstrated, that if the Fermi level in the graphene channel belongs to energy intervals, where the graphene band spectrum, modified by EuO, becomes sharply spin-asymmetric, such a device can be an ideal non-volatile spin filter. The practical application of the system under consideration would be restricted by a Curie temperature of a ferromagnet. Controlling of the Fermi level (e.g. by temperature that changes ferroelectric polarization) can convert a spin filter to a spin valve.

A hybrid of nanomagnetic Fe3O4 and antibacterial nanomaterial such as Ag is one of the promising nanoparticles for magnetoresistance-based biosensor. Therefore, we are developing a biosensor system to quantize the biomolecule concentration via the Fe3O4/Ag nanohybrid detection using a spin-valve thin-film sensing element. In this research, Fe3O4/Ag magnetic nanohybrid was synthesized using the co-precipitation/aqua-solution method. During induced by the low magnetic field (about 10-15 Gauss), the step-like magnetoresistance change of the spin-valve sensing element was observed. Embedding of Ag on the Fe3O4 magnetic nanoparticle induces 32% of magnetization saturation reduction which successfully enhances the magnetoresistance ratio by 3%. The spin-valve thin-film sensing element exhibits the linear decreasing of the magnetoresistance ratio as the increased nanoparticle concentration of Fe3O4/Ag is attached on its surface. Furthermore, the stray-field presence from Fe3O4/Ag nanohybrid is also indicated by the switching magnetic field shifting. By linking to the specific receptor agent, the Fe3O4/Ag nanohybrid can be assigned as a biocompatible magnetic label in its merger with spin-valve thin-film for magnetic-based biosensor application.

In the Micromagnetic study, current induced magnetization precession dynamics led by Spin Transfer Torque [STT] in a Spin Valve Device [SVD] is investigated numerically by solving the Landau Lifshitz Gilbert Slonczewski [LLGS] equation via Object Oriented Micro Magnetic Framework [OOMMF]. The bottom and top ferromagnetic layers are made of Ferro-Magnetic Alloy [FMA] called EuO (i.e.) a europium chalcogenide. Here, we have introduced the Current Induced Oersted Field [CIOF] and it is generated when the spin polarized current passes through the SVD. By varying the generated Oersted Field [OF] strength (Hoe) from 0 kA/m to 30 kA/m, as an increment of 10 kA/m the frequency tunability is achieved. The result imputes that, if we increase the OF strength from 0 kA/m to 30 kA/m frequency keeps on increasing, but the PSD reduces. At 0 kA/m (in the absence of the OF), 27 GHz frequency with 0.042 (arb. unit) is obtained. On the other hand, at 30 kA/m (in the presence of the OF), 34 GHz frequency with 0.021 (arb. unit) is obtained. The obtained results shown here promote the future application of SVD in spintronic devices.

Spin valve effect driven by current-induced spin–orbit torques can help to realize electrically controllable and miniaturized two terminal spintronic devices. Here, we show that in a perpendicularly magnetized Fe1−x1Tbx1/Pt/ Fe1−x2Tbx2 spin-valve multilayer, spin currents from dual surfaces of the inserted Pt layer can be used to generate spin torques that can separately switch the adjacent ferrimagnetic Fe1−xTbx layers. In a two-terminal device, we further show that the accompanied parallel and anti-parallel magnetization configurations between the two Fe1−xTbx layers can lead to the observation of the current-in-plane giant magnetoresistance (CIP-GMR). Our results demonstrate that the current-induced spin–orbit torques can be implemented into two-terminal spin-torque devices, which can be electrically read out by the CIP-GMR. The present study could be important for designing miniaturized spintronic devices.

In the present work, we have reported the results based on the effect of Bi-Quadratic Coupling [BQC] as well as the Orange Peel Coupling [OPC] in different Heterogeneous based Spin Torque Nano Oscillator [STNO] device. STNO, comprised of trilayer (X/Cu/Py) (i.e) two ferromagnetic layers separated by a non magnetic spacer. Those Ferro Magnetic [FM] layers are called fixed and free, because the corresponding magnetization tends to be fixed and free. Throughout the macro magnetic framework, Cu is taken as the non magnetic spacer and Py is taken in free layer. X (= Fe and Co) denotes the FM taken in the pinned layer for both the BQC and OPC coupling mechanism. The magnetization switching dynamics of the free layer for all devices are studied by solving the governing Landau-Lifshitz-Gilbert-Slonczewski [LLGS] equation. For all the four devices, switching time is calculated in the presence and absence of both BQC and OPC separately. The switching time for BQC based device [Co/Cu/Py] is calculated as 136 ps and 166 ps in the presence and absence respectively. Similar results are found in another BQC based device [Fe/Cu/Py]. The calculated switching time for the device is 135 ps and 181 ps in the presence and absence respectively. As far as the OPC is concerned, the switching time for the device [Co/Cu/Py] is found to be 111 ps and 160 ps in the presence and absence respectively. Relatively, other OPC based device [Fe/Cu/Py] switches 113 ps and 163 ps in the presence and absence respectively. The results depicts that OPC based devices switches rapidly as compared to BQC based devices which are highly applicable in ultra high density recording media.

We propose a method to control a bilayer superconducting spin valve (SSV) which does not perturb its superconducting state and is suitable for energy saving cryogenic electronics. This SSV consists of a superconducting layer and a helimagnetic layer of B20 family compounds, namely, Nb and spiral antiferromagnet MnSi. Thanks to unique properties of MnSi—broken inversion symmetry and cubic crystal lattice—there are a few ground state magnetic configurations with different directions of the magnetic spiral, divided by a potential barrier. Superconductivity in such a bilayer is controlled by the reorientation of the spiral vector in the MnSi layer, which leads to a change in the critical temperature of the Nb layer due to the proximity effect. The switching is proposed to be carried out by a several hundred ps in duration magnetic field pulse of several kOe in magnitude. Such a pulse does not destroy the superconducting state of the Nb layer by itself but leads to the excitation of magnons in the MnSi layer, which triggers the reorientation process of the magnetic spiral. After the completion of this process, the Nb layer switches into a normal state. Inverse switching returns the spiral to the initial state, opening the valve and turning on the superconducting state. The system can be switched there and back by a magnetic field of opposite signs along one direction in the layers plane, which allows an easy control. The switching time is estimated as several nanoseconds, which coincides with the scales of the STT-MRAM recording time.

This Letter reports an original spin valve device that is based on a chiral templated nickel material. Chirality in Ni is induced by exploiting co-electrodeposition of an organic chiral template. In this specific case, the chiral templating is enantiopure tartaric acid (TA). Facile electrodeposition (co-deposition) in ambient conditions produces a nickel chiral-templated material. Z-shaped magnetoresistance curves, switching sign as a function of TA handedness, prove the peculiar ferromagnetic character induced by the presence of a chiral compound. Synchrotron measurements using circular polarized light, x-ray natural circular dichroism, confirm the chirality of the Ni in the TA/Ni composite. Density functional theory calculation proves the existence of a strong electronic delocalization involving the tartaric acid and Ni. The significant finding of this Letter is that chiral templated Ni paves the way for future spin valve, which will be able to control the spin without an external magnetic field (as indeed foreseen within the chiral induced spin selectivity-effect framework).

Using vertical spin-valve devices, we experimentally investigate the room-temperature spin diffusion length in an undoped p-Ge layer grown on ferromagnetic Fe 3Si. Because low-temperature molecular beam epitaxy techniques enable us to grow vertically stacked and all-epitaxial CoFe/Ge/Fe 3Si trilayers on Si(111), we can intentionally vary the thickness ( t Ge) of the intermediate undoped p-Ge layer during the growth. With decreasing t Ge, the magnitude of the spin signals gradually increases at room temperature. From the analysis based on the model by Fert and Jaffres, the room-temperature spin diffusion length in the undoped p-Ge grown on Fe 3Si is experimentally estimated to be ∼ 8.4 nm, much shorter than those reported in previous works on commercial p-Ge substrates.

A heterostructure consisting of a cuprate superconductor YBa2Cu3O7-δ and a ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve was studied using SQUID magnetometry, ferromagnetic resonance, and neutron reflectometry. It is shown that because of the magnetic proximity effect a magnetic moment is excited in the superconducting portion of the heterostructure, whereas the magnetic moment in the spin valve becomes suppressed. The experimentally obtained value of a typical penetration depth of a magnetic moment into the superconductor is significantly greater than the coherence length of the cuprate superconductor, which indicates that the induced magnetic moment mechanism of Cu atoms is dominant. The mesastructure prepared by adding niobium film as a second superconducting electrode to the existing heterostructure, exhibited a superconducting current (dc Josephson effect) at interlayer thicknesses that are much greater than the coherence length of the ferromagnetic materials. The maximum of the critical current density dependence on the thickness of the spin valve material corresponds to the interlayer coherence length, which agrees with the theoretical predictions associated with spin-triplet pairing. The superconducting current is observed at magnetic fields that are two orders of magnitude greater than the field corresponding to the occurrence of one magnetic flux quantum in the mesastructure. The ratio of the second harmonic of the current-phase dependence of the mesastructure superconducting current to the first, determined according to the dependence of the Shapiro steps on the amplitude of microwave exposure, did not exceed 50%.

The equations of the microscopic theory of superconductivity in the diffusion limit (Usadel equations) are used to interpret experimental data from a study of the spin-valve effect in epitaxial Nb/Ho structures. The cause of the quasimetallic behavior of their critical dependences is determined. The influence of the triplet component of the superconducting condensate on the critical temperature is studied.

An IrMn top-nailed spin-valve multilayer film was synthesized using direct-current magnetron sputtering on a naturally oxidized silicon substrate. The multilayered film microstructure and magnetism were analyzed using x-ray diffraction, transmission, and atomic force microscopies as well as vibrating sample magnetometry as functions of ion irradiation. The reverse saturation field residence time of the spin-valve multilayered sample was used to assess its magnetic stability. Ga+ distribution in the layers after irradiation was also simulated using the SRIM2003 package. Ga+ irradiation weakened the intensity of the (111) peak of the antiferromagnetic IrMn (111) layer, decreased surface roughness as well as exchange bias field and pinned layer coercive force, while increasing the free layer coercive force. However, the multilayer exchange bias field of the spin-valve film under the reverse saturation field after Ga+ irradiation did not change with time.

We present and experimentally verify a universal theoretical framework for the description of spin-charge interconversion in non-magnetic metal/insulator structures with interfacial spin–orbit coupling (ISOC). Our formulation is based on drift-diffusion equations supplemented with generalized boundary conditions. The latter encode the effects of ISOC and relate the electronic transport in such systems to spin loss and spin-charge interconversion at the interface. We demonstrate that the conversion efficiency depends solely on these interfacial parameters. We apply our formalism to two typical spintronic devices that exploit ISOC: a lateral spin valve and a multilayer Hall bar, for which we calculate the non-local resistance and the spin Hall magnetoresistance, respectively. Finally, we perform measurements on these two devices with a BiOx/Cu interface and verify that transport properties related to the ISOC are quantified by the same set of interfacial parameters., C.S-F., F.S.B., and I.V.T. acknowledge funding from the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN) (Project Nos. FIS2016–79464-P and FIS2017–82804-P) and Grupos Consolidados UPV/EHU del Gobierno Vasco (Grant No. IT1249-19). The work of F.S.B. is partially funded by EU's Horizon 2020 research and innovation program under Grant Agreement No. 800923 (SUPERTED). The work at nanoGUNE is supported by Intel Corporation through the Semiconductor Research Corporation under MSR-INTEL TASK No. 2017-IN-2744 and the “FEINMAN” Intel Science Technology Center and by the Spanish MICINN under the Maria de Maeztu Units of Excellence Programme (No. MDM-2016–0618) and under Project Nos. MAT2015–65159-R and RTI2018–094861-B-100. V.T.P. acknowledges postdoctoral fellowship support from the “Juan de la Cierva–Formación” program by the Spanish MICINN (Grant No. FJCI-2017-34494). E.S. thanks the Spanish MECD for a Ph.D. fellowship (Grant No. FPU14/03102).

Semiconductors with strong spin-orbit interactions can exhibit a helical gap with spin-momentum locking opened by a magnetic field. Such a gap is highly spin selective as a result of a topologically protected spin-momentum locking, which can be used for spin filtering. We experimentally demonstrate such a spin filtering effect in a quasi-ballistic p-type germanium/silicon core/shell nanowire (NW), which possesses a pseudo-helical gap without the application of magnetic field. Polarized hole spin injection to the NW is achieved using cobalt ferromagnetic contacts with controlled natural surface oxide on the NW as a tunnel barrier. Local and nonlocal spin valve effects are measured as the verification of polarized spin transport in the NW outside the helical gap. We electrically tune the NW into the helical gap by scanning its chemical potential with a gate. A hysteresis loop with three resistance states is observed in the local spin valve geometry, as an evidence of spin filtering in the helical gap., 5 pages, 4 figures

Two-dimensional (2D) layered materials and their heterostructures have opened a new avenue for next-generation spintronic applications, benefited by their unique electronic properties and high crystallinity with an atomically flat surface. Here, we report magnetoresistance of vertical magnetic spin-valve devices with multi-layer (ML) MoSe2 and its heterostructures with few-layer graphene (FLG). We employed a micro-fabrication procedure to form ultraclean ferromagnetic–non-magnetic–ferromagnetic interfaces to elucidate the intrinsic spin-transferring mechanism through both an individual material and combinations of 2D layered materials. However, it is revealed that the polarity of tunneling magnetoresistance (TMR) is independent of non-magnetic spacers whether the spin valve is composed of a single material or a hybrid structure, but it strongly depends on the interfaces between ferromagnetics (FMs) and 2D materials. We observed positive spin polarizations in ML-MoSe2 and FLG/ML-MoSe2/FLG tunnel junctions, whereas spin-valve devices comprised of FLG/ML-MoSe2 showed a reversed spin polarization and demonstrated a negative TMR. Importantly, in Co/FLG/ML-MoSe2/FLG/NiFe devices, the polarization of spin carriers in the FM/FLG interface remained conserved during tunneling through MoSe2 flakes in spin-transferring events, which is understandable by Julliere’s model. In addition, large TMR values are investigated at low temperatures, whereas at high temperatures, the TMR ratios are deteriorated. Furthermore, the large values of driving ac-current also quenched the amplitude of TMR signals. Therefore, our observations suggest that the microscopic spin-transferring mechanism between ferromagnetic metals and 2D materials played a momentous role in spin-transferring phenomena in vertical magnetic spin-valve junctions.

In order to utilize perpendicular spin-torque-transfer magnetic-random-access-memory (p-STT MRAM) as a storage class memory, the achievement of performing multi-level-cell (MLC) operation is important in increasing the integration density of p-STT MRAM. For a double pinned perpendicular magnetic tunneling junction spin-valve performing MLC (i.e., four-resistance level) operation, the uniformity in the resistance difference between four-level resistances was investigated theoretically and experimentally. The uniformity in the resistance difference between four-level resistances was strongly dependent on the top MgO tunneling-barrier thickness. Particularly, the most uniform resistance difference between four resistance states could be achieved at a critical top-MgO tunneling thickness (i.e., ∼1.15 nm).

Magnonic devices are promising alternatives to conventional charge-current-driven spintronic devices. As the basic unit of spintronic devices, the spin valve is of limited use in magnonics because its dynamics is rarely studied. Here, we investigate the interlayer transmission of magnons in dynamic spin valve structures using the time-resolved magneto-optical Kerr effect. Interaction between magnons and the interfacial dissipation are studied by comparing three samples with different spin valve structures. Magnons with different intrinsic frequencies have strong interactions. In contrast, magnons with similar intrinsic frequencies have relatively weak interactions. Interfacial dissipations of magnons are increased by rare earth insertion, which can reduce the interactions between magnons indirectly. This work extends the application of spin valve structures to magnonic devices beyond their conventional use.

The spin polarization factor was investigated using electrical spin injection at low temperatures in n+-Si(100)/MgO/ferromagnet lateral spin-valve devices with Co2Fe0.4Mn0.6Si (CFMS) and CoFe electrodes. CFMS films were annealed at different post-annealing temperatures (Ta). Although atomic diffusion of CFMS into the silicon channel was observed at high annealing temperatures, the CFMS device annealed at a Ta of 350 °C, clearly showing a narrow Hanle signal measured using the three-terminal Hanle effect; a consistent spin relaxation time of 7.1 ± 0.4 ns and spin diffusion length of 1.6 ± 0.2 μm were obtained at 10 K. A local three-terminal spin-valve (L-3TSV) signal from the CFMS lateral spin-valve device was obtained at about 370 μV, three times larger than that of the CoFe device. The tunnel spin polarization factor was evaluated from the L-3TSV signals by an analytical equation that considered the spin drift effect. The estimated tunnel spin polarization factor for CFMS was 45% at a Vbias of about 600 mV, while that for CoFe was 18%. This result indicates that the high spin polarization of CFMS is responsible for the large intensity of the L-3TSV signal and that CFMS is a promising FM material for electrical spin injection into silicon.

We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented.

The Landau-Lifshitz equations are generalized to the case of spin accumulation and dynamics of localized spins in the conductive magnet, in terms of the Rashba spin-orbit scattering mechanism. The effects of the spin-orbit transfer torque caused by longitudinal current flowing through the conducting heterostructure with a thin magnetic layer, on the spin state of the structure, are analyzed in the macrospin approximation on the basis of modified Landau-Lifshitz equations. It is found that the possibility of realizing the spin switch modes in the magnetic layer of the heterostructure with an easy-plane magnetic layer exists, and depends on the geometry of the magnetization, which is also the case for transverse spin-transfer torque in spin-valve structures. We built examples of diagrams of spin states on the current-field plane, that show a satisfactory agreement between the results of the experimental measurements of the critical fields and spin switching currents in the magnetic layers of asymmetric hete...

The nonlocal spin valve configuration consists of two ferromagnetic and nonmagnetic channels, which is an effective configuration for determining spin injection and accumulation. Here, we report that a reversed nonlocal spin signal was detected by changing the voltage probe configurations in graphene (Py/MgO/graphene/MgO/Py) lateral spin valves. The abnormal reversed spin-dependent nonlocal voltage is attributed to the nonuniform pinhole at the interface of the low-resistance tunnel barrier, which makes the charge current flow through the detection electrode and return to the graphene channel. We demonstrate that the channel-width induced spin-polarized current inhomogeneity significantly contributes to nonlocal resistance. A detailed description and simulated results of the tunnel junctions provide evidence for the reversal of the nonlocal voltage sign induced by the low-resistance tunnel barriers. Our work sheds light on the understanding of the spatial distribution of the spin current and the effect of the tunnel barrier, which are essential for the development of spintronic devices.The nonlocal spin valve configuration consists of two ferromagnetic and nonmagnetic channels, which is an effective configuration for determining spin injection and accumulation. Here, we report that a reversed nonlocal spin signal was detected by changing the voltage probe configurations in graphene (Py/MgO/graphene/MgO/Py) lateral spin valves. The abnormal reversed spin-dependent nonlocal voltage is attributed to the nonuniform pinhole at the interface of the low-resistance tunnel barrier, which makes the charge current flow through the detection electrode and return to the graphene channel. We demonstrate that the channel-width induced spin-polarized current inhomogeneity significantly contributes to nonlocal resistance. A detailed description and simulated results of the tunnel junctions provide evidence for the reversal of the nonlocal voltage sign induced by the low-resistance tunnel barriers. Our work sheds light on the understanding of the spatial distribution of the spin current and the effect of...

Although current in-plane giant magnetoresistance (CIP-GMR) is widely used as various magnetic field sensors, a higher magnetoresistance (MR) ratio is still required to improve their sensitivity and detectivity for certain applications. Here, we report dramatic enhancement of the MR ratio up to 26.5% in a spin valve device and 40.5% in an antiferromagnetically coupled trilayer device using fully epitaxial Co50Fe50/Cu/Co50Fe50 structures with metastable bcc-Cu spacer layers. Transmission electron microscopy analysis indicated that the metastable bcc-Cu had a perfect lattice match at the bcc-Co50Fe50/bcc-Cu interfaces. First-principles calculations showed good electronic band matching that induces a large spin asymmetry of the electron transmittance in the in-plane direction. The combination of this substantial lattice match and electronic band match is attributed to the large MR ratio, suggesting that exploring the use of metastable structure in ferromagnetic/nonferromagnetic multilayers will lead to further enhancement of CIP-GMR.

We successfully confirmed spin injection and detection in the MnAs/GaAs/InAs hybrid system on GaAs(111)B through lateral nonlocal spin valve (NLSV) measurement at 1.5 K and 77 K. Surprisingly, we found larger NLSV signals at 77 K than that at 1.5 K. This seems to be interesting behavior compared to typical temperature dependent spin injection and detection study. We studied in depth the NLSV signals to extract spin parameters such as spin diffusion length and spin injection efficiency in the hybrid system. We found spin diffusion length to be ∼10 µm and ∼7 µm at 1.5 K and 77 K, respectively, and also found spin injection efficiency to be ∼1.6% and ∼2.5% at 1.5 K and 77 K, respectively. The reason behind higher injection efficiency at 77 K comes from better impedance matching between MnAs and InAs at 77 K than that at 1.5 K due to large temperature variation of MnAs resistivity.We successfully confirmed spin injection and detection in the MnAs/GaAs/InAs hybrid system on GaAs(111)B through lateral nonlocal spin valve (NLSV) measurement at 1.5 K and 77 K. Surprisingly, we found larger NLSV signals at 77 K than that at 1.5 K. This seems to be interesting behavior compared to typical temperature dependent spin injection and detection study. We studied in depth the NLSV signals to extract spin parameters such as spin diffusion length and spin injection efficiency in the hybrid system. We found spin diffusion length to be ∼10 µm and ∼7 µm at 1.5 K and 77 K, respectively, and also found spin injection efficiency to be ∼1.6% and ∼2.5% at 1.5 K and 77 K, respectively. The reason behind higher injection efficiency at 77 K comes from better impedance matching between MnAs and InAs at 77 K than that at 1.5 K due to large temperature variation of MnAs resistivity.

We report on the direct observation of the magneto-Peltier effect in a current-in-plane giant magnetoresistive (CIP-GMR) spin valve. By means of the recently developed thermoelectric imaging technique based on lock-in thermography, we demonstrate that thermoelectric cooling and heating are generated by applying a local magnetic field to the CIP-GMR spin-valve film, confirming the different Peltier coefficients of the spin valve between the parallel and antiparallel magnetization configurations. The cooling and heating positions are found to be tuned simply by changing the magnitude of the local magnetic field. This versatile and reconfigurable thermoelectric conversion functionality may provide a thermal management method for CIP-GMR magnetic sensors.We report on the direct observation of the magneto-Peltier effect in a current-in-plane giant magnetoresistive (CIP-GMR) spin valve. By means of the recently developed thermoelectric imaging technique based on lock-in thermography, we demonstrate that thermoelectric cooling and heating are generated by applying a local magnetic field to the CIP-GMR spin-valve film, confirming the different Peltier coefficients of the spin valve between the parallel and antiparallel magnetization configurations. The cooling and heating positions are found to be tuned simply by changing the magnitude of the local magnetic field. This versatile and reconfigurable thermoelectric conversion functionality may provide a thermal management method for CIP-GMR magnetic sensors.

Spin relaxation properties of π-conjugated organic semiconductors are key indicators of the performance of organic spintronic devices. However, reliable determination of spin relaxation parameters in organic materials is hindered by complex interfacial phenomena at organic/ferromagnetic metal interfaces that couple spin injection with charge injection. Here, we study the spin pumping induced pure spin transport in Permalloy/rubrene/Pt trilayers and determine the spin diffusion length λs = 132 ± 9 nm and the spin relaxation time τs = 3.8 ± 0.5 ms in rubrene films at room temperature by using the inverse spin Hall effect. The determined spin diffusion length λs is found to be almost two times larger than that of ∼46.3 nm at 100 K extracted from rubrene spin valve devices in which charge carrier injection/detection occurs at organic/ferromagnetic metal interfaces. Our results demonstrate experimentally that the efficiency and the rate of spin polarized charge transport through the organic/ferromagnetic metal interface play a dominant role in determining the spin relaxation process of spin valve devices in which charge and spin currents are coupled.

Spin voltages due to Hanle spin precession in a two-terminal (2T) device, composed of a silicon channel and two ferromagnetic tunnel contacts (Fe/MgO), are observed and explained. The 2T Hanle signals contain not only contributions due to spin transport from one electrode to the other but also local contributions from the spin accumulation in the Si created and detected at each of the two contacts separately. Consequently, the salient features of the 2T Hanle signals differ from those in nonlocal devices and the familiar correspondence between Hanle and spin-valve signals is absent. The local and transport contributions to the 2T Hanle signal can be disentangled and described by the same set of device parameters as the nonlocal Hanle signals.

We have demonstrated that the strain direction can be detected sensitively using an exchange-biased spin valve (SV) formed on a flexible substrate. The flexible giant magnetoresistive SV used here contains a strain-sensitive Co free layer and a strain-insensitive exchange-biased NiFe pinned layer. The exchange bias is imparted from an antiferromagnetic FeMn layer stacked on the NiFe layer. When the strain is applied in a direction deviating from the exchange bias field, the free layer magnetization rotates along this directly only, resulting in a resistance change. Compared to the previously reported flexible pseudo SV, the present device allows strain direction sensing at a much smaller strain magnitude because no external magnetic field assistance is needed to fix the pinned layer magnetization, which hampers the rotation of the free layer magnetization. The robustness of the exchange bias to the strain in the simple NiFe/FeMn bilayer structure is also discussed.We have demonstrated that the strain direction can be detected sensitively using an exchange-biased spin valve (SV) formed on a flexible substrate. The flexible giant magnetoresistive SV used here contains a strain-sensitive Co free layer and a strain-insensitive exchange-biased NiFe pinned layer. The exchange bias is imparted from an antiferromagnetic FeMn layer stacked on the NiFe layer. When the strain is applied in a direction deviating from the exchange bias field, the free layer magnetization rotates along this directly only, resulting in a resistance change. Compared to the previously reported flexible pseudo SV, the present device allows strain direction sensing at a much smaller strain magnitude because no external magnetic field assistance is needed to fix the pinned layer magnetization, which hampers the rotation of the free layer magnetization. The robustness of the exchange bias to the strain in the simple NiFe/FeMn bilayer structure is also discussed.

The spin valve effect driven by the magnetic field in sandwich structures stands out as a seminal phenomenon in the emerging field of spintronics, but it has not been realized in low-power-dissipation devices operated via electrical means. Here, we investigate spin-orbit torque switching in a perpendicularly magnetized CoFeB/Mo/CoFeB sandwich, where the spin current generated in the Mo layer flows upward and downward to the ferromagnetically coupled CoFeB layers. When scanning the current, two CoFeB layers can be switched from one antiparallel state to a parallel state and then to the other antiparallel state, producing an unprecedentedly current-dependent spin valve effect. Such a spin valve effect is sensitive to the additional magnetic field direction due to the small spin torque efficiency and efficiency difference of the two CoFeB layers. The experimental observations are supported by the dynamics simulation based on the Landau-Lifshitz-Gilbert equation. Besides the fundamental interest, our finding would add a different dimension to energy efficient memory devices and sensors.

We report the temperature dependence of the effective spin-mixing conductance between a normal metal (aluminium, Al) and a magnetic insulator ($\text{Y}_3\text{Fe}_5\text{O}_{12}$, YIG). Non-local spin valve devices, using Al as the spin transport channel, were fabricated on top of YIG and SiO$_2$ substrates. By comparing the spin relaxation lengths in the Al channel on the two different substrates, we calculate the effective spin-mixing conductance ($G_\text{s}$) to be $3.3\times10^{12}$~$\Omega^{-1}\text{m}^{-2}$ at 293~K for the Al/YIG interface. A decrease of up to 84\% in $G_\text{s}$ is observed when the temperature ($T$) is decreased from 293~K to 4.2~K, with $G_\text{s}$ scaling with $(T/T_\text{c})^{3/2}$. The real part of the spin-mixing conductance ($G_\text{r}\approx 5.7\times10^{13}~ \Omega^{-1}\text{m}^{-2}$), calculated from the experimentally obtained $G_\text{s}$, is found to be approximately independent of the temperature. We evidence a hitherto unrecognized underestimation of $G_\text{r}$ extracted from the modulation of the spin signal by rotating the magnetization direction of YIG with respect to the spin accumulation direction in the Al channel, which is found to be 50 times smaller than the calculated value.

Single-particle excitations in quasi-one dimensional ferromagnetic spin chains located in nonuniform magnetic fields with large gradients are examined. Spin waves are dynamically localized in a magnetic field with a constant gradient and a system of local levels with equidistant energies develops with a form similar to the Wannier-Zeeman “ladder.” This effect is similar to Bloch oscillations of an electron in a weak electric field. In a semi-infinite chain the spectrum of spin excitations is bounded below; with increasing energy a gradual transition from spin waves in a uniform magnetic field to states with Bloch-like oscillations occurs. An infinite spin chain in a magnetic field that is constant for x 0 is considered. Under these conditions a system of local Wannier-Zeeman states develops above the spin wave zone; their spectrum becomes equidistant at high energies. Possibilities for the experimental observation of Bloch oscillations of spin waves are discussed.

In all-perpendicular spin valve nanopillars the probability density of the free-layer magnetization is independent of the azimuthal angle and its evolution equation simplifies considerably compared to the general, nonaxisymmetric geometry. Expansion of the time-dependent probability density to Legendre polynomials enables analytical integration of the evolution equation and yields a compact expression for the practically relevant switching probability. This approach is valid when the free layer behaves as a single-domain magnetic particle and it can be readily applied to fitting experimental data., 2 figures, 5 pages, double column

Magnetoresistive sensors with high thermal robustness, low noise and high spatial resolution are the answer to a number of challenging applications. Spin valve sensors including MnNi as antiferromagnet layer provide higher exchange bias field and improved thermal stability. In this work, the influence of the buffer layer type (Ta, NiFeCr) and thickness on key sensor parameters (e.g. offset field, Hf) is investigated. A Ta buffer layer promotes a strong (111) texture which leads to a higher value of MR. In contrast, Hf is lower for NiFeCr buffer. Micrometric sensors display thermal noise levels of 1 nT/Hz1/2 and 571 pT/Hz1/2 for a sensor height (h) of 2 and 4 μm, respectively. The temperature dependence of MR and sensitivity is also addressed and compared with MnIr based spin valves. In this case, MR abruptly decreases after heating at 160°C (without magnetic field), contrary to MnNi-based spin valves, where only a 10% MR decrease (relative to the initial value) is seen at 275°C. Finally, to further decrease the noise levels and improve detectivity, MnNi spin-valves are deposited vertically, and connected in parallel and series (in-plane) to create a device with low resistance and high sensitivity. A field detection at thermal level of 346 pT/Hz1/2 is achieved for a device with a total of 300 SVs (4 vertical, 15 in series, 5 in parallel).

Bloch–Bloembergen–Slonczewski (BBS) equation is established by extending Bloch–Bloembergen equation, and it is used to study magnetization oscillation in the free magnetic layer of a magnetic tunneling junction. Since both short–wavelength magnon excitation and spin–transfer torque are taken into account in the BBS equation, it is distinguished from Landau–Lifshitz–Gilbert–Slonczewski equation. The macro–spin BBS model predicts that the transverse relaxation time in free magnetic layer should be long enough, as compared with the longitudinal relaxation time, to achieve stable magnetization oscillation for spin–transfer torque oscillator application. Moreover, field–like torque favors the tolerance of fast transverse relaxation, which makes magnetic tunneling junction a better choice than spin valve for the spin–transfer torque oscillator application.

Giant magneto-resistance (GMR) spin-valve films with an FeSiB/CoFeB free layer were fabricated to detect applied strain in a GMR device. The magnetostriction constant of FeSiB was experimentally determined to have 32 ppm, which was one order of magnitude larger than that of CoFeB. In order to detect the strain sensitively and robustly against magnetic field fluctuation, the magnetic field modulation technique was applied to the GMR device. It was confirmed that the output voltage of the GMR device depends on the strain, and the gauge factor K = 46 was obtained by adjusting the applied DC field intensity and direction. We carried out the simulation based on a macro-spin model assuming uniaxial anisotropy, interlayer coupling between the free and pin layers, strain-induced anisotropy, and Zeeman energy, and succeeded in reproducing the experimental results. The simulation predicts that improving the magnetic properties of GMR films, especially reducing interlayer coupling, will be effective for increasing the output, i.e., the gauge factor, of the GMR strain sensors., ファイル公開：2019-03-21

We theoretically study magnon transport in an insulating spin valve (ISV) made of an antiferromagnetic insulator sandwiched between two ferromagnetic insulator (FI) layers. In the conventional metal-based spin valve, the electron spins propagate between two metallic ferromagnetic layers, giving rise to giant magnetoresistance and spin transfer torque. Here, the incoherent magnons in the ISV serve as angular momentum carriers and are responsible for the angular momentum transport between two FI layers across the antiferromagnetic spacer. We predict two transport phenomena in the presence of the temperature gradient: a giant magneto-spin-Seebeck effect in which the output voltage signal is controlled by the relative orientation of the two FI layers and magnon transfer torque that can be used for switching the magnetization of the FI layers with a temperature gradient of the order of 0.1 Kelvin per nanometer.

Graphene is an ideal material for spintronic devices due to its low spin-orbit coupling and high mobility. One of the most important potential applications of graphene spintronics is for use in neuromorphic computing systems, where the tunable spin resistance of graphene can be used to apply analog weighting factors. A key capability needed to achieve spin-based neuromorphic computing systems is to achieve distinct regions of control, where injected and detected spin currents can be tuned independently. Here, we demonstrate the ability to achieve such independent control using a graphene spin valve geometry where the injector and detector regions are modulated by two separate bottom gate electrodes. The spin transport parameters and their dependence on each gate voltage are extracted from Hanle precession measurements. From this analysis, local spin transport parameters and their dependence on the local gate voltage are found, which provide a basis for a spatially-resolved spin resistance network that simulates the device. The data and model are used to calculate the spin currents flowing into, through, and out of the graphene channel. We show that the spin current flowing through the graphene channel can be modulated by 30% using one gate and that the spin current absorbed by the detector can be modulated by 50% using the other gate. This result demonstrates that spin currents can be controlled by locally tuning the spin resistance of graphene. The integration of chemical vapor deposition (CVD) grown graphene with local gates allows for the implementation of large-scale integrated spin-based circuits.

The electric conductivity of point nanocontacts between 5, 10, and 100nm thick ferromagnetic (F) cobalt films and a nonmagnetic (N) metal (copper or silver) needle is investigated. Two fundamentally different mechanisms for the formation of the response signal to microwave irradiation have been observed for the first time. One mechanism is due to the effect of the rectification of high frequency ac current on the nonlinearity of the current-voltage characteristics due to the precession of the magnetization under the action of a constant transport current flowing through the contact. The second one is associated with the resonance excitation of the precession of the magnetization vector at the fundamental frequency and its harmonic by an external high-frequency field. The experimental results support a previous contention that a “surface spin valve” whose static and dynamic properties are similar to conventional F1–N–F2 spin valve [Nano Letters 7, 927 (2007)] is formed in the experimental F–N nanocontacts.

The propagation of spin waves in Q2D layered conductors placed in a magnetic field is studied. It is shown, that at certain orientations of the magnetic field with respect to the layers the collisionless absorption is absent and weakly damping spin waves can propagate even under the strong spatial dispersion. We have analyzed the spectrum of spin modes at an arbitrary form of Landau–Silin correlation function.

Large spin-transfer effects were observed in spin-valve pillars developed for current-perpendicular-to-plane (CPP) magnetoresistive heads. The investigated samples are complex stacks including laminated free, synthetic/laminated pinned, and nano-oxide layers. The magnetoresistive (MR) transfer curves exhibit current-dependent loop shift and in some particular ranges of current and field, very large noise associated either to stochastic jump of the free layer magnetization or to excitations of steady precessional modes. A very unusual phenomenon of inverted coercivity was observed in the low current range. The spin-transfer effects show an asymmetry as a function of current direction. These experimental results indicate that the spin-transfer effects must be considered in the design of CPP MR heads.

We have explored phenomenological temperature dependence of hot electron magnetotransport in a spin valve transistor. We stress spin polarization of hot electrons and spatial inhomogeneity of Schottky barriers to explain the peculiar temperature and spin dependence of collector currents. Qualitative trends are established for collector current with changes in temperature, thickness of spin-valve base, along with height and width of Schottky barriers.

We confirmed that the location of a specularly reflective oxide layer is critical to enhance the giant magnetoresistance effect in a spin valve. In particular, embedding an oxide layer in the pinned layer is more effective than placing oxide on top of the free layer to increase the giant magnetoresistance values when the free layer is thick, and this makes the spin valve robust for high density magnetic recording. This behavior can be explained by the mirror effect that arises as a result of the structure of the spin valve.

Spin-valve structures might be exposed to higher temperatures in future disk drive applications and might thus degrade faster than it does today if proper materials and methods are not used. In order to determine whether this degradation is due to interdiffusion between constituent layers or is dominated by other phenomena, the interdiffusion coefficients for all layers in the spin valve have to be determined. For diffusion driven degradation it would then be possible to predict lifetimes based on a maximum allowed reduction in ΔR/R where R is the resistivity. Here we report the initial results for a CoFe/Cu interface, common to many spin-valve structures. Interdiffusion in (111) textured polycrystalline CoFe/Cu multilayers has been measured and quantified by x-ray reflectometry. Bulk diffusion is dominant at temperatures above ∼540 °C and is described by an activation energy of Ea=2.41 eV and a prefactor of D0=2.92×10−8 m2/s. Below temperature of 540 °C grain boundary diffusion dominates and is character...

On-chip spin-valve sensors (2×6 μm2) were used to detect the binding of streptavidin-functionalized superparamagnetic labels to sensor surface-bound biotin. Both micron-sized and nanometer-sized labels were studied. The detection of biomolecular recognition was demonstrated using 2 μm Micromer®-M and 250 nm Nanomag®-D labels, with signals ranging from ∼300 μV to ∼2 mV (8 mA sense current; ∼15 Oe in-plane magnetizing fields). For smaller labels, detection of biomolecular recognition was not achieved. The capability of detecting single labels was demonstrated for label moments down to 2×10−12 emu (2 μm labels), corresponding to signals of 100–400 μV. Although, theoretical calculations suggest that the minimum measurable moment is in the order of 6×10−15 emu, due to noise limitations of the present setup, this limit is in the order of 2×10−13 emu, corresponding to a single 250 nm label. On-chip tapered aluminum current line structures were used for placement of magnetic labels at sensor sites.

A two terminal spin-injection device is fabricated using a nanostencil process with a Co–Cu–Co stack. The stack can be deposited both by sputtering and by electron-beam evaporation. A better edge definition is observed in evaporation-deposited films under cross section transmission electron microscopy. Both methods succeeded in producing junctions with sub-100 nm lateral dimensions and show spin-injection-induced magnetic switching.

High-frequency measurements of spin-valve films and devices, made using several different measurement techniques, are presented and compared. Pulsed inductive measurements were made on sheet films and provide insight into the intrinsic dynamical properties of the component films and multilayer stacks. The damping parameter, in the completed spin-valve stack, is larger than in the constituent films. Direct time and frequency domain measurements of the dynamical response of micrometer-size spin-valve devices, made using high-bandwidth magnetoresistance techniques, showed damping parameters comparable to these measured on spin-valve sheet films. The small-angle magnetization response was also determined by high-frequency magnetic noise measurements. The damping parameters were smaller than those obtained by direct susceptibility measurements. The device-level measurements show a different dependence of the damping parameter on the easy-axis field as compared to sheet-level measurements. In addition to the un...

We found that capping a spin valve with thin oxide can make the interlayer coupling oscillatory as a function of thickness of the Cu spacer. The coupling was antiferromagnetic and it allowed us to reduce the thickness of the Cu spacer down to 20 A without sacrificing the good properties of the spin valve. In addition, the oxide layer enhanced specular reflection of conduction electrons at the interface. As a result, we could greatly increase the giant magnetoresistance (GMR) value of the spin valve. The fact that less current shunted through the thinned Cu spacer and the enhancement of specular reflection contributed to the large GMR value. We also report the observation of the oscillation of interlayer coupling as a function of thickness of the magnetic layer in a spin valve.

The magnetic domain structures and magnetization reversal of patterned 70-nm-wide pseudo-spin-valve (PSV) elements were studied by magnetic force microscopy (MFM). Both magnetically soft and hard layers form single-domain states at remanence, and can be magnetized either parallel or antiparallel to each other. The switching field of each layer, and the coupling between the layers, are quantified using MFM. Individual elements show well-defined switching fields, while the ensemble has a large switching field distribution due to variability between the PSV elements.

By extending a previous semi-classical model, we investigate the effects of inserting a second ferromagnetic material at the interface or in the interior of the ferromagnetic layer in NiFe/Cu/NiFe and/or Co/Cu/Co sandwiched structures on their giant magnetoresistance (GMR). The calculated GMR was found to be consistent with experimental results, indicating that our model is applicable even for complicated spin-valve multilayers. Moreover, some theoretical predictions are given in this letter that allow us to propose ways to optimize spin-valve structures.

Two sets of NiFe/FeMn films with Ta and Ta/Cu buffer layers were prepared by magnetron sputtering. Results show that the exchange bias field of NiFe/FeMn films with a Ta/Cu buffer is lower than that of the films with a Ta buffer. The crystalline texture, surface roughness, and element distribution of these two sets of samples were examined, and there is no apparent difference for the texture and roughness. However, the segregation of Cu atoms on the surface of NiFe in the trilayer of Ta/Cu/NiFe has been observed by using the angle-resolved x-ray photoelectron spectroscopy. The decrease of the exchange bias field for NiFe/FeMn films with a Ta/Cu buffer layers is mainly caused by the segragation of Cu atoms to the surface of the NiFe layer.